Letting your feet dry out over night certainly helps, but it won't necessarily prevent trench foot. I managed to develop it over the course of a single long day back in 2000 (before the days of Hydropel -- or at least I didn't know about it then). I was walking along the PCT in Washington. Although I started the day with dry feet, it was raining, and my shoes got soaked. I kept going up over passes where it was snowing, and then down into valleys where it was raining, and my feet stayed very wet and very cold all day; not cold enough for frost bite, but definitely cold. That night I got to a town and got a hotel room. My feet felt more sore than usual, but I didn't think anything of it until I woke up in the middle of the night to find my feet throbbing, twice their normal size and bright red with white splotches. Couldn't walk on them at all for a couple days and had to end a thru-hike because of it.
My take-away is that drying out your feet at night will work to prevent trench foot in normal temperatures, but if it is wet and cold out, you need to find a way to keep your feet warm, like by using a goretex sock to trap heat or something.